There is a growing need for polycarbonates with a heat of performance greater than commonly obtained with amorphous polycarbonates. Such prior art polycarbonates have a glass transition temperature (Tg) of about 150.degree. C. Because of high heat performance required in today's applications for thermoplastics, a polycarbonate having a higher Tg is wanted while still retaining the same or better optical and mechanical properties as is well known with aromatic polycarbonates.
Several attempts have been made to prepare polycarbonates having a higher heat of performance (i.e. a higher Tg). Recent commercialization of copolymers of bisphenol-A and bisphenol-fluorenone was undertaken but was not successful.
Bi-phenol and (6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiindane (hereinafter "SBI") have been used along with Bisphenol-A in making polycarbonate with higher Tg. Due to the rigidity and stiffness of the aforementioned comonomers, microcracking of molded parts was a major issue. Furthermore, the high cost of bisphenol and spirobiindane (SBI) raise the cost of polycarbonates prepared therewith.
Consequently, various issues, including deleterious physical properties and/or cost have precluded the commercialization of higher Tg polycarbonates or copolymers.